NASA is preparing to launch a first-time-ever effort to keep an American astronaut in space for a whole year.

The mission is in preparation to one day send human beings to Mars and beyond.

What makes this trip even more historic is that it will include, also for the first time, identical twin brother astronauts.

Commander Scott Kelly will soon be in space onboard the International Space Station while his twin brother, retired astronaut Mark Kelly, will stay home on Earth.

The brothers are almost identical genetically, so scientists will be able to measure how Scott reacts physically and emotionally to long-term exposure to the extremes of space and then compare that to earthbound Mark.

"If we're ever going to leave low-Earth orbit, there are a lot of negative effects that we need to understand and have mitigations to those or it's going to be very, very difficult for us to send people on a trip to Mars and back or somewhere else," Scott explained.

Zero gravity can have a terrible effect on the human body, causing weaker muscles, more brittle bones and a weaker heartbeat, not to mention the issue of radiation.

This mission is expected to give NASA scientists unprecedented insight into those effects.

To date, Mark has logged 54 days in space as a shuttle commander and pilot. Scott has completed 180 days, and if he returns as scheduled in a year, that number jumps to 540, a NASA first.

"It's great to see my brother have the opportunity to fly in space again," Mark said. "This is a historic, important mission, and I expect we're going to learn a lot from it."

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